For analysis of molecular motions in solids, liquids and gases, dielectric measurement utilizing a uniform electric field is widely employed. In general, molecules can be classified into a polar molecule having no symmetry center but having an electric dipole moment, and a nonpolar molecule having a symmetry center but having no electric dipole moment. When permittivity of solid or liquid containing a polar molecule with a degree of freedom of internal rotation is measured as a function of frequencies by utilizing the conventional method for measuring an electric response of a substance under a uniform electric field, a graph shown in FIG. 10 is obtained. As shown in FIG. 10, a dielectric loss exhibits a peak and a permittivity then decreases at a critical frequency fc at which a molecular rotational motion becomes unable to follow a time change in alternate current. Thus, from the dielectric measurement data, information on the molecular motion can be obtained. According to the conventional measuring method utilizing a uniform electric field, it is possible to analyze a motion of a polar molecule having an electric dipole moment, whereas it is not possible to analyze that of a nonpolar molecule having no dipole moment.
In order to measure the motion and relaxation of a nonpolar molecule unresponsive to suchlike dielectric measurement, optical methods such as Raman scattering and neutron inelastic scattering method have been employed. The optical methods utilize visible light (1014 Hz) and hence a relaxation phenomenon observable by the optical method is limited, thereby making it difficult to measure phenomena occurring at 1011 Hz or less. Besides, the neutron inelastic scattering method utilizes neutrons with the number of vibrations in the order of 1012 Hz, and hence, it is difficult for the current technologies to detect motions slower than those occurring at 1010 Hz or less due to energy resolution.
See, “Solid-State Science” by Ryou Sakata, published by Baifukan Co., Ltd. in 1989, p 221; “Materials Structure and Introduction to Dielectric” by Masaaki Takashige, published by “Shokabo Publishing Co., Ltd.” in 2003, p 46; and “Raman Spectroscopy” edited by Hiro-o Hamaguchi and Akiko Hirakawa, published by “Japan Scientific Societies Press” in 1994.
The conventional method utilizing a uniform electric field is suitable to detect the motion of a polar molecule with the dipole moment. In nonpolar composite molecules where the dipole moments are combined with the polarities opposed to each other, however, forces acting on the dipole moments cancel each other to thereby permit no interaction to occur between the directions of the electric field and the molecular axes, thus making it impossible to detect the motion of the nonpolar molecule by the uniform electric field method. It is an object of the present invention to provide a method for electrically detecting a motion of such nonpolar composite molecule. The term “composite molecule” mentioned here means an atom cluster comprising a plurality of atoms in the broad sense.